Method of assembling main reduction gears



15, 1946. F. E. FREEMAN METHOD OF ASSEMBLING MAIN REDUCTION GEARS Filed June 14, 1944 2 Sheets-Shet 1 ATTORNEYS Jan. 15, 1946. F. E. FREEMAN 2,393,098

' METHOD OF ASSEMBLING MAIN REDUCTION GEARS Q Filed June 14, 1944 2 Sheets-Sheet 2 INVENTOR FRANK E. FREEflAN PM W ATTORNEYS Patented Jan. 15, 1946 AssE BLING MAIN I Rubric:- TION GEARS Frank-Everett Freeman, -Bath'.Maine i AppIicati'onJ'une 14, 1944, Serial No. 540.283 j METHOD" OF FFi-iC V 1 Claims. (Cl.:29 -159.2)

This invention relates to improvements in the assembling of main reduction gears "of the lock train type." More particularly the irlVI'ltlOhT- lates to improvement inthe assembling'o'f the lock train type of main'redu'ction gears used on shipboard for'driving the propeller shaft by high speed and lowspeed turbines.

' The new method of the present invention enables the main reduction gears'to be"ass'embled with a radical reduction in time required and with corresponding saving'of laboras comparedwith the methods heretofore employed in assembling main reduction gears on'ships' such as U. S. Navy destroyers.

. In the propulsion of ships by means'of steam" turbines the main reduction gears serve to reduce the high speed of the turbines to that of the-propellers; A large main or bull gear is mounted on the propeller shaft and is provided with a thrust bearing to take care of the propeller thrust;' and betweenlthis main or bull gear and the turbines are double reduction gears of the lock train type. With" high pressure and low pressure turbine drives; each turbine is connected to a high speed pinion which in turn drives the first reduction pinions mounted on shafts carrying the second reduction pinions which mesh with the main ear. Thesegears are commonly of the double helical type with one right'and "one left hand helix to eliminate-end thrust and to give an' equal distribution of pressure over the entire length of the gears. With high speed and low speed turbines 'each having driving pinions connected totwo reduction pinions, there are four reduction pinions meshing with the main or bull gear and distributed around the upper portion of this gear at different angular locations and at diiferent elevations.

It has heretofore been the practice to install these reduction gears by the piece by piece assembly aboard ship. With a large-main or'bull gear upwards of 7' in diameter and with an overall assembly weighing around 15 tons or more the time required for assembling the gear has been around 40 hours.

.The improved process of the present invention enables the time required for assembling the main reduction gears on shipboard to be radically reduced e. g. to less than 4 hours time.

I have found that the entire reduction gear assembly which is to be connected with the main or bull gear can be assembled at the place of manufacture and installed aboard ship without disassembly; and that such installation-"can readilyflbe accomplished without injurytothegears and even though the pinions which are to mesh? with the main gear are to be located at different levels "and with different radial arrangement onthe'main gear. It is necessary to complywith certain fea tures of procedure'in order-to eifectsuch assembly Without injury'to the gear teeth.-

According to the present inventi'omthe assembled reduction gears of the lockflt'raintype'are loweredinto place and brought into engagement with the main gear by a series of lowering steps and by rotation of the pinions to predetermined positions and as a part of the successive'lowerin'g steps; B-y-such careful and predetermined frotation' of the-pinions and by taking advantageof the backlash in the gear train, the various pinion although at-different levels and "with different angular arrangement around the main gear can be brought into proper enmesh'mentwith the main;

gear during the lowerin injuryto the'gear teeth.

In carrying outthe improved method of the present invention the lower case, containing the bull gear and its journal-bearings. and the main thrust-hearing, is assembled-aboard ship inthe usual manner. 7 The upper assembly, however; in-

g operation and without stead of bein'g J installed piece" by piece' on shipboard; is assembled complete; except for :covers, in theshop at theplace of manufacture Thus thefirst'reduetionand the second reduction-minions' are assembled com'pIete :the upper: case with bearings and bearing caps before placing the up'per Tease aboard ship. This asse'mbly,-ialthough it may weigh several tons,v can be.-readi1y transported and lowered into theengine ro'omrby a dock crane or by other handling equipment. This'assembly is then lowered and placed in position above andspaced apart fromits final lowered position. erg, where the teeth of the gears have adepth of-about .450" theassembly is lowered to'withinabout 1'" of its final position. e.g., by inserting'steelblocks one inch" square by afoot long on' the lower case and lowering the: assembly-so thatit rests on. these blocks. This i'enables the case tobe brought into proper alignment and insures parallelism of the two jointfaces.

In order to insure engaging in the proper-position, two marks are advantageously made on each lowe'r second reduction' pinion while 'theassembly is still in the shop: Proper aligning marks may also advantageously 'be put on' the for-wardiends 'of the ifirstreduction' pinions and gears. These marks correspondzto the twopositions .to which the lower secondreduction pinions are rolled durmg the :first loweringcstepi of the "process" and-the late'z final positionfduringithe completedi-lowering corresponds to step. The marks are so placed that as the lower pinions are lowered during the first step they have been rotated to a position which is unsuited for final engagement but which enables the preliminary lowering of the upper casing and gears to be accomplished without injury to the gear teeth. After this first lowering step the upper reducing pinions are rotated to a point that is suitable for bringing the teeth into engagement and the lowering is then completed, the backlash of the'gear train and the rotation of the gears bringing the pinions at different levels and different angular relations into proper alignment with the main gear without injury to the gear teeth.

The invention will be further illustrated and described in connection with the accompanying drawings which show in. a somewhat conventional and diagrammatic manner the gears of a destroyer and illustrate the method of installation of the main reduction gears.

Inthe accompanying drawings: Fig. 1 is a plan with parts broken away showing the assembled gears;

Fig. 2 is an elevation with parts broken away; Fig. Sis a somewhat diagrammatic view showing one step in the lowering of the upper casing and gear assembly;

Fig. 4 shows one of the lower pinions just before engagement withthe main gear;

Fig. 5 shows the same pinion rotated to its final position; 7

Fig. 6 is a diagrammatic view showing the marking of the first reduction and driving pinions; I

Fig. '1 illustrates the location of the gear teeth after the upper casing has been lowered to a predetermined position and before the subsequent lowering steps; v

Fig. 8 shows the arrangement of the gearing teeth of one Of the pinions at a later lowering stage; and

1 Fig. 9 shows the arrangement of the teeth after the pinion has been lowered to its final position.

In the accompanying drawings the lower case the preliminary lowering step. Similar marks C and D may be placed on the front ends of the first reduction gears or pinions and driving pinion as shown in Fig. 6.

The upper assembly of reduction gears fabri- I cated outside the ship and lowered into a place above that of its final position is illustrated in Fig. 2, the upper frame and assembly being supported by jack screws 3| operating in holes in the'upper casing or frame 21; The upper assembly may thus be lowered by a crane or by chain falls with the aid of guide pins to within one inch of its final position and supported on steel blocks one inch square by a foot long to insure that the upper case is parallel with the lower case. Four jacking screws 3| are then used to take the weight of the assembly off the spacer blocks and the blocks are then removed. leaving the jacking screws supporting the upper assembly as illustrated in Fig. 2. Special jacking screws are advantageously used of standard thread, with a fiat top, case hardened, and with the head'marked off in numbered quarters. They should be about 2%" in length under the head.

With the weight of the upper assembly supported on the four jacking screws and the oneinch blocks removed, the assembly is then lowered by four men turning the jack screws in unison. The heads of the screws are marked off in numbered quarters and each man turns his screw it quarter of a turn at a time, keeping even with for the main or bull gear 2 is indicated at I and has bearings 4, and 5 for the shaft 3 of the bull gear which shaft is connected by the coupling 1 with thepropeller shaft 8. The end thrust bearing for taking up the propeller thrust is indicated at 8. V s

The upper casing 9 has assembled therein a high speed pinion 10 with shaft 'H adapted to be connected'to ahigh pressure turbine and a high speed pinion l2 similarly adapted to; be connected with a low pressure turbine b'y shaft 13;

Thetwo high speed pinions Ill and 12 are each connected with two first reduction gears l5, l6, l9 and 20 and the shafts of these first reduction gears ll, l8, 2| and 22 carry at their other ends reduction pinions 23, 24, 25 and, 2B; or are connected with the shafts of these secondreduction pinions. The four last mentioned pinions 23, 24, 25 and 26 are those which are to mesh; with the main or bull gear 2 when the assembly isproperly' lowered into place.

The cover frame 9 has a lower frame No. '21

and cover No. 28 united at the joint flange 29.

In order to control the position of the pinions while they are being lowered two marks are placed on each of the lower pinions as shown e. g. at A and B on pinion 26 in'Figs. 4 and 5. One mark corresponds to the final position of the pinion when lowered into place. .The other mark the rotation of the pinion duringthe other three men. The lower pinions will engage first with the bull gear when the upper case is within about iii" of the lower case and the upper pinions will engage at approximately in the case of gears having teeth .450" in depth.

Before any of the teeth of the pinions come in contact with or engage the teeth of the bull gear it is important that the lower pinions be rotated a predetermined distance to a position which is not suitable for final enmeshment with the bull gear but which will permit the lowering of the assembly until the teeth of the lower pinions partly engage the teeth of the bull gear.

Inthis position the teeth of the upper pinions are not in suitable position for lowering and the first stage of lowering should be stopped before the teeth of the upper pinions engage the teeth of the main gear. After this preliminary lowering the upper pinions are rotated to a proper position for lowering, and the lowering is then completed. The backlash in the gear train together with the successive adjustments and lowverings of the assembly brings the teeth of the various pinions into proper enmeshment with the teeth of the bull gear even though the pinions are located at different levels and in different angular relations such that the normal enmeshment of the gears are at widely, varying angles from each other.

The marks A and B shown in Figs. 4 and 5 are marks indicating the predetermined positions of the lower pinion. When the mark B is in line with the joint flange 29 as shown; in Fig.

4 the pinion is rotated to the position suitable for the first lowering step. The mark A when in alignment with the joint flange 29 shows the final position of the pinion when it has been rolled back and is in full engagement with the 1 gear. 7

The position of the teeth of the lower pinion ,beforeit is lowered and which permits it to be lowered part way is illustrated in Fig. 'I while Figfd indicates the position of the teeth. after the first lowering step. The teeth in this position permit rolling of the pinion back to a position approximating its final position while the further lowering and rolling that takes place incidental thereto brings the teeth into proper position.

The rolling of the teeth of the lower pinions for the first step of the lowering process moves the teeth of the upper pinion out of proper position. Accordingly, after the first lowering step and before the uppers engage they should be rolled to take advantage of the backlash in the gear train. From the time the lower gear engages the bull gear until it is in its final position, it rolls from a position such that the lower inscribed line on its barrel is in the plane of the cover-joint face to a position such that the upper line is in that plane, these being illustrated in Figs. 4 and 5. Due to the location of the upper pinions they should not roll once they are engaged. To allow the upper pinions to remain in their engaging position while the lower pinions roll, in spite of the fact that they are part of a locked train, the upper is rolled upward before engagement. Then the rotation delivered from the lower is taken up by the backlash and does not affect the upper.

When the upper case has been lowered into its final position the gears are checked for proper engagement and the entire assembly is then ready for bolting up and covers. This assembly, less main covers and end covers, weighs around 15 tons.

The marking of the reduction gears to indicate the positions of predetermined rotation of the gears during assembly is advantageously made in the shop before the upper assembly is lowered into the ship. The bull or main gear or its coupling flange is similarly marked at the factory for a predetermined position for assembly and the bull gear when installed in the lower casing is adjusted to the predetermined position and left in place so that the teeth of the pinions when set in predetermined position will mesh therewith, during the successive steps, without injury to the gear teeth.

The present method enables a radical reduction to be accomplished in the time required for installing the reduction gear assembly, From the time the gear is picked up on the dock the assembly can be lowered into place in about an hour and usually less than four hours is required from the picking up Of the gear to the completion and checking and covering up of the completed assembly; whereas some 36 to 40 hours or more were commonly required in the assembly of the gears n shipboard according to the common practice. While time is required for assembling the reduction gears in the factory or in the shop, this can be done much more readily than in the cramped conditions of a ships hold or engine room; while the short time required for installing the assembled gears avoids interference with other ship construction which would otherwise be delayed or restricted by the long time required in installing the reduction gears.

The short time required for installing and closing the unit greatly reduces the danger of injury by loose material falling into the gears. The time formerly required for installing the gears and which interfered with or prevented other operations of the ship construction is by the present invention made available for other work which would otherwise be delayed. Thus the present invention not only makes possible a great saving in the time of installation of the reduction gears but makes possible the expedition of other work in the area where the assembly has been completed.

In addition to the time saved in the shipyard in installing the reduction gears, there is also a considerable saving on the part of the gear manufacturer since the unit may be shipped almost immediately after running the final tests and without the need of disassembling the gears for shipment and reassembling on shipboard.

I claim:

The method of assembling double reduction gears of the lock train type with a large main driven gear on shipboard for driving the propeller shaft by high speed and low speed turbines which includes assembling in an upper rigid frame the reduction gear trains each including a high speed driving pinion meshing with two first reduction gears which in turn drive reduction pinions which are to drive the main gear and which are to mesh with the upper portion thereof at different angular locations and at higher and lower levels, lowering the frame carrying the gear trains to a position above the main gear without engagement of the reduction pinions and main gear, rotating the lower reduction pinions of the trains to predetermined positions away from that of their final engagement to permit partial engagement, lowering the frame to a limited extent to cause such partial engagement without engagement of the upper reduction pinions with the main gear, rotating the upper reduction pinions to approximately their positions of final engagement, and completing the lowering of the frame to bring both the upper and lower reduction pinions into final engagement with the main gear.

FRANK EVERETT FREEMAN. 

